This invention relates to calibrated gas metering devices, and particularly those devices applicable to provide a precisely calibrated therapeutic oxygen flow in a portable oxygen supply kit adapted to be carried by an ambulatory patient to supply a prescribed rate of oxygen to such patient. More particularly, the present invention relates to an improved seal apparatus for use in a selective control valve which is used in such metering devices to selectively provide a plurality of accurate oxygen flow rates.
Oxygen supply kits for ambulatory patients are known and in use. They include an indexing control valve which is movable to a plurality of positions, each providing a different flow rate. For example, the control valve can be set to deliver 1, 2, 3, 4, and 5 liters per minute. Such flow rates are obtained by passing the gas at a regulated pressure through metering orifices in a metering disk. In one application, such rates required metering holes having diameters, respectively, of approximately 0.006, 0.009, 0.011, 0.013, and 0.015 inches. The orifices had been formed by drilling these small holes in the metering disk or inserts in the metering disk mechanically or by an EDM process. Such drilling does not provide sufficient accuracy, and when the EDM process is employed, it is necessary to allow a margin of error of plus or minus 10% of the desired flow rate. See, for example, U.S. Pat. No. 3,949,966.
A conventional gas metering valve includes a valve body having an inlet and an outlet with a dividing wall therebetween, the dividing wall including a metering element having a first and second hole therein, which first and second holes intersect and together define a passageway for gas flow from the inlet to the outlet. A ball of a diameter approximately equal to the diameter of the first hole is press-fitted into the first hole so as to be positioned therein solely by the fitting engagement of its surface with the wall of the first hole. The ball is positioned adjacent the intersection of the first and second holes so as to define a region in the passage having a cross-sectional area less than the cross-sectional area of either the first or second hole. By manipulating the position of the ball while monitoring the flow of gas through the passage., the ball can be positioned at a location which will achieve the desired gas flow rate. Desirably, the first hole is several times larger and preferably four or more times larger than the second hole. On the one hand, this facilitates handling and insertion of the ball, and on the other hand, facilitates formation of a gas passage providing the desired small and accurate gas flow rate. A plurality of such first and second holes can be provided, each set of a first and a second hole defining a separate passage for the metered flow of gas from the inlet to the outlet. The passages thus defined are positionable in communication with the gas inlet such that only one such passage can permit the flow of gas therethrough at any one instant in time. A detent means can be provided for assuring appropriate alignment of one of said passages with respect to the gas inlet. For an example of such a gas-metering valve, see U.S. Pat. No. 4,366,947 which is incorporated herein by reference.
The metering element comprises a cylinder, and the first holes are arranged in a circle about the axis of rotation of the cylinder and extend linearly through the cylindrical element parallel to the axis of rotation. The second holes extend radially from the cylindrical surface of the element to the point of intersection with the first holes. The balls are press-fit from one face of the cylinder to the point of intersection of the first and second holes, each ball being positioned at a slightly different location so as to achieve a different flow rate through each passage thus formed.
To assure proper alignment of the cylindrical metering element, a circular race is provided in one end of the element, the race being in registry with the circular arrangement of first holes. A detent means comprising a spring-biased ball is arranged in rolling frictional engagement in the race to effect an arresting action in any rotation of the cylindrical element, the detent means being so situated as to cause selected alignment of a single first and second hole pair to provide a passage between the inlet and outlet of the gas-metering valve.
Conventional gas metering valves include a two piece seal arrangement located between the metering element and the valve body. This two piece sealing arrangement includes a sealing disk and a separate O-ring for holding the sealing disk against the metering element. One problem associated with this conventional arrangement is that the O-ring may be compressed during operation of the valve to restrict or block gas flow from the gas inlet through the aperture of the sealing disk and into the passageway of the metering element.
The improved seal apparatus of the present invention advantageous provides a seal between the movable cylindrical metering element and the valve body. The improved seal apparatus includes a plastic sealing disk having an aperture formed therethrough. The disk is also formed to include a notch or recessed portion surrounding the aperture for receiving an O-ring therein. Therefore, the O-ring is nested within the plastic sealing disk. The improved configuration of the seal apparatus of the present invention advantageously limits compression of the O-ring to a predetermined amount. By limiting compression of the O-ring, the improved seal apparatus of the present invention advantageously reduces the likelihood that the O-ring will block flow of gas from the gas inlet through the aperture formed in the sealing disk and into the passageway of the metering element.
According to one aspect of the invention, an improvement is provided for use in a calibrated gas metering valve including a valve body having a gas inlet and a gas outlet, and a metering element located therebetween. The metering element includes a passageway formed therethrough to permit gas flow through the passageway from the gas inlet to the gas outlet. The improvement comprises a cylindrical sealing disk formed to include an aperture aligned with the passageway and the gas inlet to permit gas flow through the sealing disk. The sealing disk provides a seal between the valve body and the metering element. The sealing disk is formed to include a recessed portion surrounding the aperture. The improvement further includes an O-ring located in the recessed portion of the sealing disk to limit compression of the O-ring to a predetermined amount.
The sealing disk includes an inner wall defining the aperture and an outer wall. In one illustrated embodiment, the recessed portion for receiving the O-ring is formed in the sealing disk adjacent the inner wall. In another illustrated embodiment, the recessed portion for receiving the O-ring is formed in the sealing disk adjacent the outer wall. In another illustrated embodiment, the recessed portion is an annular trough formed in the sealing disk between the inner and outer walls for receiving the O-ring.
According to another aspect of the present invention, a gas metering valve is provided for selectively providing a series of different calibrated gas flow rates. The valve includes a valve body having a gas inlet, a gas outlet, a chamber situated between the gas inlet and gas outlet. The valve also includes a metering element located in the chamber. The metering element is formed to include a plurality of passageways for permitting gas flow from the gas inlet to the gas outlet. The metering element is movable relative to the valve body to position a selected passageway in communication with the gas inlet. The valve further includes a seal apparatus including a sealing disk in sliding contact with the movable metering element. The sealing disk has an aperture formed therethrough aligned with the gas inlet for sealing said chamber against the transmission of gas therethrough except when the metering element is oriented with the selected passageway in registry with the aperture in the sealing disk. The sealing disk is also formed to include a recessed portion surrounding the aperture. The seal apparatus also includes an O-ring located in the recessed portion of the sealing disk for engaging the metering element to assure constant frictional engagement between the metering element and the sealing disk.
In the illustrated embodiment, the metering element is cylindrical and rotatable within the chamber of the valve body about an axis of rotation. The plurality of passageways are arranged about the axis of rotation and extending linearly through the cylindrical metering element parallel to the axis of rotation.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of the preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.